1. Field of the Invention
The present invention relates to a knocking control device for a multicylinder engine. More particularly to a knocking control device for a multicylinder engine which can reliably control knocking in all of the cylinders of the engine by providing a single knock sensor for any one of the cylinders.
2. Description of Background Art
It is known that when the ignition timing of an internal combustion engine is earlier than a fundamental ignition timing, an output from the engine is increased, but knocking is prone to occur. Accordingly, the engine output can be improved by advancing the ignition timing from the fundamental ignition timing in such a correction range that knocking does not occur. Conventionally, a knock sensor is used to detect the occurrence of knocking, and the ignition timing is advanced in the range that knocking does not occur, thereby improving the engine output.
However, a knock sensor is expensive, so that if a plurality of knock sensors are respectively provided for all of the cylinders of a multicylinder engine, an increase in cost of a vehicle having the engine is invited. More particularly in a compact vehicle, the space around the engine is limited, so that there is a case where it is difficult to ensure an installation space for each knock sensor or there is a case where the installation space for each knock sensor may cause a large limitation to the layout of other parts. Further, such a problem becomes more remarkable with an increase in number of the cylinders of the multicylinder engine.
In relation to this problem, Japanese Patent Laid-open No. 2002-155795 discloses a technique for detecting the occurrence of knocking in a multicylinder engine by using a single knock sensor.
Vibrations are produced in the engine by various factors. Accordingly, in performing knocking control such that the occurrence of knocking is detected according to vibrations produced in the engine, it is desirable to provide a knock sensor on the side surface of a cylinder block in order that knocking vibrations can be selectively detected. Accordingly, in the case of detecting the occurrence of knocking in a multicylinder engine by using a single knock sensor, it is important to consider the location of the knock sensor to be provided in the vicinity of any one of the cylinders.
In Japanese Patent Laid-open No. 2002-155795, however, although the occurrence of knocking in the multicylinder engine is detected by using the single knock sensor, the consideration on the location of the knock sensor is insufficient.